<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>02-js控制结构和样式</title>
  <!--    <style>
          #demo{
              width: 100px;
              height: 100px;
              background-color: palegreen;
          }
      </style>-->
  <style>
    div {
      background-color: aqua;
    }
  </style>

</head>
<body>
<div id="demo"></div>
<div class="test"></div>
<script>
  var obj = document.getElementById("demo");
  obj.style.width = "200px";
  obj.style.height = "200px";
  obj.style.backgroundColor = "red";
</script>
</body>
</html>